Diagnosis of meningitis in immunocompromised hosts, such as those with AIDS or cancer, is difficult because of the unavailability of sensitive methods for detecting the most likely pathogens. Organisms in these settings, such as cytomegalovirus (CMV), Herpes simplex virus (HSV), and Varicella-Zoster virus (VZV), are difficult to grow from CSF, and no good antigen detection techniques are available. Over the past few years, it has become increasingly clear that detecting these viral agents with polymerase chain reaction (PCR) methodology may provide the most sensitive and specific diagnostic tests. These tests may soon become the method of choice. Therefore, we are developing in-house PCR procedures that will become available as a service. We have had to select primers and optimize amplification parameters for each of the viruses, because there are no commercially available amplification kits or standardized methods accepted. At present we have PCR assays under way for each of the three viruses, and are in the process of final validation of each. For diagnostic service use, we must determine the analytical sensitivity and the specificity of each assay. Because the test has been developed in-house, we must also have data to validate its performance on patient specimens. As part of this development, we are investigating practical alternatives to southern blots for specific identification of the PCR product to simplify and shorten the overall procedure. For this investigation, we are experimenting with the use of the Delfia fluorometric assay, using europium-labeled probes to detect the amplification product. If this detection assay is reliable and sensitive, it will provide a rapid method for identifying the PCR product.